SELAGINELLA 163 



Alps to the Arctic regions, and is abundant in Scottish 

 and Irish mountains. The spores produced by the 

 Lycopodiacese are of one size; they give rise to various 

 forms of prothalli, which in some instances are small, 

 colourless, tuberous structures growing underground, 

 and are saprophytes accompanied by a fungus. Male 

 and female organs occur on the same prothallus, the 

 antheridia being sunk in the tissue, while the archegonia 

 rather resemble those of Ferns. 



Psilotocece. — A family with two genera. Psilotum 

 grows on tree-trunks and branches in the tropics. Its 

 stem is angular and forking; its leaves are much reduced, 

 and scalelike. It is a delicate plant, and has no roots. 

 Tmesipteris is found in Australia and New Zealand; it 

 has lengthy trailing stems, furnished with pointed 

 leaves ; it also is an epiphyte. 



SelaginellacecB. — The largest family of the group, but 

 its 500 species are all included in the one genus — Selagi- 

 nella. The majority of the species are tropical; one is 

 abundant in the European Alps, Selaginella helvetica 

 (Fig. 52), and S. selaginoides, or spinosa, called the 

 " Lesser Club-Moss," or " Prickly Mountain-Moss," is 

 found in the North of England, in Wales, Scotland, and 

 Ireland, in wet stony places, and in boggy places by 

 mountain-streams. An enlarged drawing of a fertile 

 spike of this species is reproduced in Fig. 53. This 

 solitary British representative of the Selaginellas differs 

 from most of its relatives in having leaves arranged 

 round the stem; the majority of the species produce 

 shoots with four rows of leaves, two of them arranged 

 one on either side of the edges of the stem, and two on 

 either side of a middle line on the upper surface of the 



